When to Plant Onions
Published: April 21, 2026
Onion timing is determined by day-length as much as frost dates. Use short-day varieties south of 35°N latitude (TX, FL, CA) and long-day varieties north of 35°N (OH, MN, NY).
When to plant onion
- Start seeds indoors: 10 weeks before last frost
- Direct sow outdoors: 4 weeks before last frost
- Minimum soil temperature: 35°F
- Days to harvest: 90–120 days
- Sun requirement: Full sun
- Spacing: 4 inches apart
- Water: 1 inches per week
- Fall crop: No — single spring/summer crop only
⚠ CRITICAL: Choose variety based on your latitude. Short-day varieties for south of 35°N (Texas, Florida, California). Long-day varieties for north of 35°N (Ohio, Minnesota, New York). Intermediate varieties work in the middle band.
Growing Tips for Onions
- •Match variety to latitude: short-day south of 35°N, long-day north of 35°N, intermediate in between.
- •Growing from sets (small bulbs) is fastest; growing from transplants gives the most variety options.
- •Reduce watering as tops begin to fall over — dry conditions encourage tight, firm bulbs that store longer.
- •Cure harvested onions 2–4 weeks in a warm, dry, airy location before storing — uncured onions rot quickly.
Companion Planting for Onions
✅ Plant onion with
- • Carrot
- • Tomato
- • Lettuce
- • Beet
- • Chamomile
❌ Avoid planting near
- • Bean
- • Pea
- • Asparagus
Common Onion Pests and Problems
Regional pest pressure varies — see your state guide below for state-specific pest calendars and treatment timing.
Onions Planting Dates by State
Select your state for exact sow and transplant dates based on local frost calendars.
Frequently Asked Questions
What onion variety do I need?
Onion variety selection is determined by latitude. South of 35°N (Texas, Florida, most of California): use short-day varieties like Texas 1015, Granex, or Yellow Bermuda. North of 35°N (Ohio, Minnesota, New York): use long-day varieties like Walla Walla, Yellow Sweet Spanish, or Copra. Middle band: intermediate varieties work well.
When do I start onion seeds indoors?
Start onion seeds indoors 10–12 weeks before your transplant date — onions are one of the earliest indoor starts of any vegetable. In most regions this means starting seeds in January or February for spring transplanting.
When can I transplant onions outside?
Transplant onion seedlings 4–6 weeks before your last frost date. Young onions tolerate hard frost down to 20°F. Setting them out in cool early spring conditions allows them to establish well before the long days that trigger bulbing.
When do I harvest onions?
Harvest when 50–75% of the tops have fallen over naturally — do not rush. Bend the remaining upright tops over by hand to speed the process. Dig carefully to avoid bruising. Cure for 2–4 weeks in a warm, dry, well-ventilated area before long-term storage.
What grows well with onions?
Onions are strong companion plants — they deter carrot fly, aphids, and a range of pests. Plant with carrots, tomatoes, and lettuce for mutual benefit. Chamomile planted among onions is said to improve flavor. Avoid planting near beans and peas which are inhibited by onion root compounds.